A mordenite (MOR) type molecular sieve (Na8[(Al8Si40)O96].24H2O), which pertains to the orthorhombic system having a space group of Cmcm and lattice parameters of a=18.3 Å, b=20.5 Å, c=7.5 Å and has a tunnel structure of [001] 12 6.5 Å×7.0 Å-[010] 8 3.4 Å×4.8 Å-[001] 82.6 Å×5.7 Å, is one kind of the important catalytic and adsorption-separation materials, as applied widely in the petroleum processing and fine chemistry industries such as xylene isomerization, transalkylation, toluene disproportionation and selective hydrogenation of olefins.
The prior-art MOR type molecular sieves are generally prepared through a conventional hydro-thermal synthesis process in a system with high alkalinity, by providing a silicon source by silica powders, sodium silicate, silica sols or the like, and providing an aluminum source by sodium metaaluminate, aluminum sulfate or the like.
A MOR type molecular sieve is synthesized using sodium aluminate (32.6 wt % Na2O, 35.7 wt % Al2O3) and SiO2 powders as raw materials at a molar ratio of 6Na2O:Al2O3:30SiO2:780H2O by Kim and Ahn (Kim G J., Ahn W. S. Direct synthesis and characterization of high-SiO2-content mordenites. Zeolites, 1991, 11, 745-750), which is characterized by XRD to have main peaks at d=3.45, 3.97, 9.02, 3.27 and 3.21 Å and have a composition, as the product, of Na2O:Al2O3:17.2SiO2.
CN 88100228A discloses a method for synthesizing a mordenite in non-aqueous systems, which uses water glass and aluminum sulfate as silicon and aluminum sources and an organic phase as a dispersion medium, and comprises firstly synthesizing a aluminosilicate gel in an oriented manner, then dispersing the gel into an organic medium, and subjecting the dispersion to polycondensation, nucleatation and further crystallization to produce the mordenite.
CN 1050011A discloses a method for synthesizing a high-silicon mordenite, comprising directly synthesizing a high-silicon mordenite having a SiO2-to-Al2O3 ratio of 15-30 under the presence of ammonia with water glass, an inorganic acid/base and an aluminum salt or aluminate as raw materials.
CN 1463921A discloses a method for synthesizing a high-silicon mordenite, comprising producing a mordenite in a hydro-thermal synthesis at 110-230° C. with salts or oxides of silicon and aluminum, and hydroxides of an alkali metal as raw materials and a neutral substance, caprolactam, as a templating agent.
Although the technologies for synthesizing a molecular sieve with chemical agents as raw materials are well-developed, the chemical agents such as water glass, sodium silicate and aluminum sulfate are generally derived from natural silicon-containing or aluminum-containing minerals through complicated processes, which associated with huge waste generation and extensive energy consumpsion. Therefore, direct synthesis of a molecular sieve from natural aluminosilicate and silicate minerals through a “green” method can not only shorten the synthesis route, but also widen the sources for synthesizing a molecular sieve due to the various types and plentiful reserves of natural silicon and aluminum minerals.
Currently, the reports of synthesizing a molecular sieve with natural aluminosilicate minerals as raw materials are mainly focused on Y and ZSM-5 zeolites which synthesized with natural kaolin as raw materials. There are also reports on studies for preparing a molecular sieve with natural aluminosilicate minerals, such as montmorillonite or diatomaceous earth, as raw materials.
However, when a molecular sieve is synthesized with natural aluminosilicate minerals such as kaolin, rectorite, diatomaceous earth or montmorillonite as raw materials, the natural aluminosilicate minerals mostly have to be activated by high-temperature calcination having a temperature of 600-1000° C., which is a high energy-consumed activation process.